Background

Blades are getting longer and slenderer, and therefore more flexible in torsion (twist).
Blades are aeroelastically tailored to twist when they bend. This twist reduces aerodynamic forces when a wind gust hits the blade.
The structural integrity of such blades is dependent on this load mitigation – getting the twist coupling wrong will cause blade failure.
Validations of the blade torsion stiffness in the test stand and the bend-twist coupling in the prototype field test require accurate methods for blade bending and twist measurements.
By enabling on the fly measurement of blade torsion and bend it is possible to decrease the safety margin and thereby increase output from existing wind turbines

Existing Solutions

All current methods for measuring bending and twist of blades in operation on a turbine are based on image processing of pictures taken of different types of targets on the blades. This includes solutions from Siemens, Boulder Imaging, Berlin Wind and Qualisys
For these solution the image processing is done offline after the campaign of taking the pictures.
Sampling rate is typically below 5 Hz due to need for high resolution.
High data storage required.

Technology Overview

The two active targets, such as Infra-Red (IR) light sources, are mounted in a blade section emitting frequency-modulated light. The modulation ensures that they can be distinguished from each other and ambient light ().
The light sources can be either battery powered or connected to a self-generating power source.
A Position Sensitive Device (PSD) is used instead of a camera, tracking the positions of these light sources, whereby no image processing is needed; deflections and twist can be computed instantly in real-time with the same sampling rates as turbine load measurements (30 – 50 Hz).
A Proof of Concept project at SDU during 2020 has shown that the measurement method works indoor over a 10-meter distance.
The output of the system are directly timed series of deflections and twist, thus the requirement for data storage is minimal and validations of the measurement is instant.
The expected resolution of this system is about 1 mm for a blade length of 100 meter and scales accordingly with blade length.
The system can be extended with extra light sources along the blade span to measure the spanwise distributions of deflection and twist during blade operation.

Benefits

The technology has several benefits over existing technologies:

It is easier to install than existing technologies
It can provide measurements in several sections of the wind turbine blade
It requires less data handling capacity
It provides higher frequency and accuracy than existing technologies
Data can be evaluated near real time

Applications

Building into new wind turbines for constant monitoring
Test setups for new prototypes

Opportunity

Prior art exist for technologies that can measure torsion (twist) and bending of wind turbine blades. However, none of these utilize the frequency modulation that makes this version resilient towards other ambient light sources such as the sun. Thus, a patent application focusing on different ways of implementing this feature in a functional and practical manner () has been submitted for national phase in US, CA, CHINA and EPO. EPO evaluation in PCT phase was ‘all claims novel and inventive’. The patent application was updated before national phase with latest research data from Proof-of-Concept (PoC) project where a prototype was built in 1:10 scale. The results were added to the PCT application and included extensive insights regarding:

How to avoid noise from other light sources such as the sun
How to choose optimal frequencies for modulation
More qualified description on the type and placement of the light sources and cameras

The application was also updated based on input from industry regarding the market relevance for the product.Also results from tests with two different industry partners have been added to the applications. Based on the results of the PoC project and the confirmation obtained from industry parties, it is evident that a product based on the elements of this patent application is relevant.

Blade Motion Tracker

Patents

IP Status

Seeking